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Titolo:
INFLUENCE OF PHOSPHATE AND PH ON MYOFIBRILLAR ATPASE ACTIVITY AND FORCE IN SKINNED CARDIAC TRABECULAE FROM RAT
Autore:
EBUS JP; STIENEN GJM; ELZINGA G;
Indirizzi:
FREE UNIV AMSTERDAM,INST CARDIOVASC RES,DEPT PHYSIOL,VAN DER BOECHORSTSTRAAT 7 1081 BT AMSTERDAM NETHERLANDS
Titolo Testata:
Journal of physiology
fascicolo: 3, volume: 476, anno: 1994,
pagine: 501 - 516
SICI:
0022-3751(1994)476:3<501:IOPAPO>2.0.ZU;2-Z
Fonte:
ISI
Lingua:
ENG
Soggetto:
SKELETAL-MUSCLE FIBERS; NUCLEAR MAGNETIC-RESONANCE; RABBIT PSOAS FIBERS; INORGANIC-PHOSPHATE; SARCOPLASMIC-RETICULUM; ADENOSINE-TRIPHOSPHATASE; ACTOMYOSIN SUBFRAGMENT-1; MECHANICAL-PROPERTIES; CONTRACTILE FAILURE; INHIBITION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
48
Recensione:
Indirizzi per estratti:
Citazione:
J.P. Ebus et al., "INFLUENCE OF PHOSPHATE AND PH ON MYOFIBRILLAR ATPASE ACTIVITY AND FORCE IN SKINNED CARDIAC TRABECULAE FROM RAT", Journal of physiology, 476(3), 1994, pp. 501-516

Abstract

1. The effects of inorganic phosphate (P-i) and pH on maximal calcium-activated isometric force and MgATPase activity were studied in chemically skinned cardiac trabeculae from rat. ATP hydrolysis was coupled enzymatically to the breakdown of NADH, and its concentration was determined photometrically. Measurements were performed at 2.1 mu m sarcomere length and 20 degrees C. ATPase activity and force were also determined when square-wave-shaped length changes were applied, with a frequency of 23 Hz and an amplitude of 2.5 %. 2. At pH 7.0 without added P-i, the average isometric force (+/- S.E.M.) was 51 +/- 3 kN m(-2) (n = 23). The average isometric ATPase activity was 0.43 +/- 0.02 mM s(-1) (n= 23). During the changes in length ATPase activity increased to 152 +/- 3 % of the isometric value, while the average force level decreased to 48 +/- 2 %. 3. Isometric force gradually decreased to 31 +/- 2% of the control value when the P-i concentration was increased to 30 mM. Isometric ATPase activity, however, remained constant for P-i concentrations up to 5 mM and decreased to 87 +/- 3 % at 30 mM P-i. When P-i accumulation inside the preparation due to ATP hydrolysis was takeninto account, a linear relationship was found between isometric forceand log [P-i]. The decrease in relative force was found to be 44 +/- 4 % per decade. 4. During the length changes, ATPase activity and average force showed, apart from the increase in ATPase activity and decrease in average force, the same dependence on P-i as the isometric values. Stiffness, estimated from the amplitude of the force responses during the length changes, decreased in proportion to isometric force when the P-i concentration was increased. The changes in the shape of theforce responses due to the repetitive changes in length as a functionof the P-i concentration were relatively small. These results suggestthat the effect of P-i on the transitions which influence ATP turnover is rather insensitive to changes in cross-bridge strain. 5. Isometric force, normalized to the control value at pH 7.0, increased gradually from 54 +/- 1 % pH 6.2 to 143 +/- 10 % at pH 7.5 ATPase activity remained practically constant for pH values from 6.8 to 7.2 but decreasedto 80 +/- 1 % at pH 6.2 and to 83 +/- 5 % at pH 7.5. ATPase activity during the length changes was reduced more than the isometric ATPase activity when pH was lowered. The average force level during length changes remained almost constant over the entire pH range. However, the shape of the force responses under acidic conditions was pH dependent. These observations suggest that at least one of the pH-sensitive transitions in the cross-bridge cycle which influence ATP turnover is dependent on changes in cross-bridge strain. 6. To mimic the changes which may occur during ischaemia, trabeculae were activated at pH 6.2 in thepresence of 30 mM P-i. These experiments showed a decrease in isometric force and ATPase activity to 14 +/- 1 % and 47 +/- 3 %, respectively. Average force and ATPase activity during the length changes decreased to 32 +/- 3 % and 55 +/- 3 %, respectively. This indicates that theconcurrent changes in [P-i] and pH cause a three- to fourfold increase in isometric tension cost.

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Documento generato il 30/11/20 alle ore 14:40:45